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File: 970613_me013_90a_txt_0001.txt
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SUBJECT:  Letter re: BW Agent Filters          

U.S.ARMY TROOP SUPPORT COMMAND
              NATICK RESEARCH, DEVELOPMENT AND ENGINEERING CENTER
REPLY TO 
ATTENTION OF
                                                    17 April 89
                                                    ME 013.90
[b.6.]
U.S. Medical Bioengineering
Research and Development Labaratory
Fort Detrich, MD

[b.6.]

In accordance with our telephone conversation l have enclosedsome of my data dealing with the environmental stability ofbotulinum neurotoxin A. I also found that staphylococcalenterotoxin A is stable when assayed by ELISA but, since we didnot use an animal assay, I did not include this information.

My concern about the definition of a filters ability to removeBW agents is due to me distinguishing between inactivatingagents such as heat, germicides, radiation, etc and byfiltration or by absorption. With the former agents it isconceptually acceptable to define a 3D, 6D or 12D decrease inthe initial population as the reduction of 3,6, or 12logarithmic cycles of organisms, agents, etc. It is also highlylikely that this reduction occurs in every portion of thesample.To increase lethality one increases the temperature,concentration, etc. The correct determination of the end pointis, of course, a statistical requirement.

When it comes to filters I find myself thinking, not In termsof lethality, but In terms of efficiency. I believe that aconceptual relationship must be (or perhaps already has been )established between lethality and efficiency. These are thequestions that I have and they are derived from examining theresults obtained from the NLabs supported filter studies. 

1 . If 103/ml of biological units are used to challenge afilter and some of the biological units pass through the filterln the initial 100 ml the units is considered to besatisfactory since a 99.9% reduction was obtained. This is notreally an acceptable definition of sterility. What appears tobe involved is the probability of a biological test unitpenetrating a defect.
3. Are there models available for the evaluation of filters forsterilization studies?

These questions probably reflect my unfamiliarity andinexperience with filtering devices and I would thereforeappreciate your comments on these questions.

Sincerely yours,


[b.6.]

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